1. Field of the Invention
The present invention relates to a flow cytometer for investigating particle constituents that flow in liquids, and more particularly to an imaging flow cytometer for capturing with a video camera particles, such as blood cells in blood or cells in urine, by allowing a sample liquid prepared by diluting blood or urine specimen to pass through a transparent tube called a flow cell.
2. Description of the Background Art
In accordance with a conventional method, a sample liquid, such as blood and urine, in which cells are flowing is introduced into a flow cell having a flat cross section so that images of cells that pass through the flow cell are captured with a system combining a flash lamp and a video camera. Apparatuses for investigating urinary sediment constituents have already been developed which incorporate such an image capturing system.
Subject cells in urinary sediment range from germs and erythrocytes having a size of several .mu.m to epithelium and casts having a size of several hundred .mu.m. In microscopic investigation, the range of vision (magnification) is set to two magnification levels; a high-power field(HPF) and a low-power field(LPF).
FIG. 12 is a view illustrating the outline of a conventional imaging flow cytometer.
In FIG. 12, Reference Numeral 24 designates a flow cell, 26 a sample flow that flows in the flow cell 24, 10 a flash lamp for irradiating the flow cell 24 with light, 12 a collimator lens for rendering parallel the light coming from the flash lamp 10, 20 an iris for restricting the light, 22 a condenser lens for converging the parallel light, 28 an object lens and 54 a lens switching device. The lens switching device 54 is capable of switching between a x4 relay lens and a x1 relay lens. Reference Numeral 50 designates a video camera for capturing an image of particles in the sample flow 26, 56 an image processor for processing a particle image captured by the video camera 50.
In this manner, conventional imaging flow cytometers are provided with a plurality of magnifying relay lenses, which are physically switched to magnify particles with a desired magnification.
However,when imaging flow cytometers of these kinds magnify the power of photography in a sequence of capturing small particles, the result is that large particles are left undetected. On the contrary, when the imaging cytometers reduce the power of photography in a sequence of capturing large particles, small particles are left undetected. Thus, when small particles and large particles consecutively flow through the flow cell, the imaging flow cytometers cannot switch the magnification of the lens immediately. Therefore, such cytometers obtain only images that can be captured with the selected magnification. In other words, either the large or the small particles are left undetected in any event.
In addition, since the flash lamp 10 is flashed at equal intervals of one-thirtieth second in conformity with the frame cycle of the video camera 50 regardless of whether or not particles pass through the capturing region of the video camera 50, the imaging flow cytometers obtain many images free of the particles during examination of samples containing a small amount of particle constituents like urine. In other words, the imaging flow cytometers cannot photograph cells that pass through the flow cell 24 with certitude.
As described above, when samples contain particles having various sizes and the particle concentration is low, such as with urine, the conventional imaging flow cytometer, which can analyze only a small amount of samples as a practical matter, has a drawback of being likely to ignore clinically important cells.
The present invention has been made in view of the above, and the invention provides an imaging flow cytometer that can immediately switch the magnification of lenses depending on the size of particles even if subject samples (like urine) contain particles having different sizes ranging from several .mu.m to several hundred .mu.m. Thus such imaging flow cytometer is capable of efficiently capturing both large and small particles while switching the magnification.
The following apparatus are known which capture particle constituents in a sample liquid by allowing the sample liquid to flow through a flow cell.
At the outset, as described in Japanese Patent Publication No. HEI 3-52573, an apparatus is known which applies a strobe light to a flow of a sample liquid that flows through a flat flow cell to capture static images of particle constituents with a video camera and processes the images.
Furthermore, as described in Japanese Published Unexamined Patent Application No. SHO 63-94156, an apparatus is known which comprises an optical system for capturing a particle image downstream of an optical system which triggers the photographic system in which static images of cells are captured with the system for capturing the particle image after the cells are detected with the optical system trigger.
Still furthermore, as described in Japanese Published Unexamined Patent Application No. HEI 4-72544 and Japanese Published Unexamined Patent Application No. HEI 4-72545, an apparatus is known which comprises an optical system for detecting a particle and an optical system for capturing the particle; in which a particle detecting area and a particle capturing area are formed so that the particle detecting area traverses the particle capturing area, thereby enabling capturing of particle images as soon as particles enter the particle detecting area.
On the other hand, as described in Japanese Published Unexamined Patent Application No. HEI 3-105235, an apparatus is known which captures static images of particle constituents having different sizes by switching the magnification of the lens during the measurement of particles.